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1.
Broadband linearly polarized waveguide mode converters have been developed to transform the high-order cylindrical TEm1 output wave from harmonic gyrotron amplifiers into the more useful TE11 fundamental waveguide mode. The converter's corrugation period is equal to the beat between the two waves and the bandwidth is predicted to be inversely proportional to the number of periods. Four-period TE 31/TE11 and TE41/TE11 converters with an azimuthal perturbation of mc=4 and mc =5, respectively, have yielded a peak conversion efficiency of 98% with a bandwidth greater than 3% and a one-period beat-wave converter has been designed to yield 12% bandwidth. However, it has been observed in measurements that the strong coupling in a short converter can lead to a shift of the center-frequency with an accompanying reduction of the efficiency and bandwidth. A two-period TE41/TE11 converter with 5% bandwidth displayed a 5% frequency shift and a conversion efficiency of only 86%  相似文献   

2.
The vector finite element method is used for investigating the behavior of a set of the first higher-order, four-fold degenerate modes (TE01, TM01, and two-fold degenerate HE21 modes) of a circular core optical fiber whose core cross-section changes into an ellipse. It is found that the TE01 mode becomes the first higher-order mode polarized along the minor axis, E 21y mode, in a dual-mode region. The remaining three modes become, respectively, the first higher-order mode polarized along the major axis, E21x mode, and the second higher-order modes polarized along the major and minor axes, E12 x and E12y modes, in the order of magnitude of the effective index. It is also found that the effective index of the E21x mode is smaller than that of the E21y mode in a small ellipticity region  相似文献   

3.
近年来,为解决传统介质谐振器天线(dielectric resonator antenna, DRA)体积庞大等问题,新颖的低剖面DRA如介质贴片天线和平面介质天线被提出并迅速成为研究热点.然而,现有的低剖面DRA设计要么平面尺寸较大(>0.5λ0×0.5λ0),要么带宽较窄(<10%),限制了它们的实际应用.文中提出了一种具有小型化平面尺寸的宽带低剖面DRA.本天线采用介质贴片设计,顶部为高介电常数的介质贴片,中间为低介电常数的介质基板,底部为缝隙馈电结构.缝隙馈电结构可激励起介质贴片谐振器的基模TE111和高次模TE131两种工作模式,这两种模式的场分布在贴片边缘部分存在基模场强较弱而高次模场强较强的显著区别.本设计巧妙地利用了该区域的模式场强区别,通过略微增加贴片边缘部分高度来显著影响高次模谐振频率而轻微影响基模谐振频率,从而将高次模TE131的谐振频率迅速下拉并与基模TE111的谐振频率靠近合并,在不增大介质贴片平面尺寸的前提条件下获得宽带工作效果.本天线的三维尺寸为0.35λ0×0.35λ0×0.08λ0 (λ0为中心频率处的空气中波长),线极化实物案例测试结果表...  相似文献   

4.
Designs of compact quasi-periodic and aperiodic TE0n-TE 0n-1 circular waveguide converters for use with gyrotrons in an electron cyclotron heating (ECH) system are developed by analytically and numerically solving the coupled-mode differential equations. Quasi-periodic mode transducer designs which convert the TE02 mode to the TE01 mode, and in some cases also include a taper (waveguide radius reduction), are developed. A 60-GHz aperiodic mode converter-taper combines a 6.35-cm-2.779-cm waveguide diameter taper and a TE02-TE01 mode converter. A 140-GHz aperiodic mode converter-taper combines a 6.35-cm-2.779-cm waveguide diameter taper and a TE03-TE02-TE01 mode converter. The resulting designs are highly efficient (conversion efficiencies ⩾99.4%), are shorter, have a broader bandwidth than previous designs, and have a waveguide radius greater than or equal to 1.389 cm over the entire length of the transducer to allow for high-power transmission. Experimental results consistent with theoretical calculations are presented  相似文献   

5.
The propagation behavior of the four lower-order modes, HE11 , TE01, TM01, and HE21, in a radially anisotropic cylindrical waveguide with liquid crystal cladding is studied both theoretically and experimentally. The cylindrical waveguide is a doubly-clad fiber with an isotropic core and inner cladding and a radially anisotropic outer cladding made of nematic liquid crystal. Theoretically, the propagation and decay constants for the TE01 and TM01 modes are obtained by solving the wave equations exactly, while those for the HE11 and HE 21 modes are derived using perturbation techniques under the weakly guiding approximation. It is predicted that in such a structure the guided TE01 mode can be separated from the leaky HE11, TM01, and HE21 modes. The theoretical results show good agreement with the experimental observations for a 3 cm long fiber cell with a 5 μm inner cladding radius  相似文献   

6.
Theoretical and numerical results are presented on the propagation of infrared radiation in TE01-, TM01-, and TE11-like modes in an empty cylindrical, gold-coated waveguide of micron dimensions. Low-loss propagation is possible for the TE01-like mode, whose configuration is similar to that of the TE01 mode in a guide with perfectly conducting walls. Propagation is more lossy for the TM01- and TE11-like modes. While for small guide radii these modes resemble the TM01 and TE11 modes in a guide with perfectly conducting walls, they transform into surface waves as the guide radius is increased, with losses that are independent of guide radius  相似文献   

7.
The depolarization contents of the radiating currents on the surface of a multibeam offset parabola are minimized, for different beams, using multimode pyramidal horn feeds. Small percentages of the TE 11 and TE20 modes are used, respectively, for vertical and horizontal polarizations, in combination with the fundamental TE10 mode. The mixture ratio increases for feeds with higher pointing angles to the reflector surface. Additionally, the beams that are away from the symmetry plane, suffer changes in the polarization bearing angles, which increase for further beams. Far radiated fields are computed from the depolarization minimized reflector currents, using both the orthogonal components of the linear polarization, for a 3M offset reflector with a diameter-to-focal-length ratio of unity, at 4 GHz. Minimized depolarization levels of around -40 dB for vertical polarization, and of around -34 dB for horizontal polarization are found. The linearly and circularly polarized diagonal horn feeds yield symmetric pencil beams. Their polarization, however, is quite high and difficult to control for linear polarization. For circular polarization, to the contrary, the depolarization is quite low  相似文献   

8.
A single-period 60 GHz TE02-TE01 mode converter for use in an electron cyclotron heating (ECH) system for magnetically confined plasmas is presented. The mode converter is very compact and has a broad bandwidth and a theoretical conversion efficiency of 97.6%. A method of computing the reflection from converters is presented and used to show that reflection from the single-period mode converter is minimal. Experimental results are consistent with theoretical calculations  相似文献   

9.
A new polarimetric interferometer has been developed on the basis of the phase difference between transverse electric (TE)0 and transverse magnetic (TM)0 modes in a composite optical waveguide (OWG). The composite OWG consists of a single-mode potassium ion-exchanged planar waveguide overlaid with a high-index thin film that has two tapered ends and supports only the TE0 mode. Applying tapered velocity coupling theory, we found that the TE0 and TM0 modes coexisting in the potassium ion-exchanged layer were separated in the thin film region of the composite OWG: the TE0 mode was coupled into the thin film while the TM0 mode was confined in the potassium ion-exchanged layer. Interference occurs between TE- and TM-polarized output components when a single output beam is passed through a 45°-polarized analyzer. The phase difference φ between both orthogonal output components is very sensitive to the superstrate index nc in the thin film region. Our experimental results indicate that a slight change of Δnc=3.71×10-6 results in the phase-difference variation of Δφ=1° for a 5-mm-long TiO 2/K+ composite OWG with a 34-nm-thick TiO2 film. Such a simple polarimetric interferometer can be applied to chemical or biological sensors by modifying the upper film surface of the composite OWG with a chemically or biologically active substance  相似文献   

10.
The use of triple mode TE01δ cubic resonators for the design of transmission mode filters is presented. Frequency tuning and coupling between modes are studied experimentally. The tunability of all inter-cavity couplings, necessary for the realization of a wide range of transfer functions, is demonstrated with a 6th degree, 5 MHz wide filter at 2 GHz. With an insertion loss of 0.7 dB in a volume of 260 cm3, the filter presents a 2:1 volume reduction over conventional TE01δ filters  相似文献   

11.
An efficient method for the determination of the scattering matrix of TE11-to-HE11 corrugated cylindrical waveguide mode converters has been developed, based on the representation of the fields inside the corrugations by a small number of radial waveguide modes. Numerical results show that the method, when compared to the usual mode-matching techniques, reduces the computation time without loss of accuracy  相似文献   

12.
韩凯  崔文达  奚小明  李志鸿 《红外与激光工程》2020,49(4):0405001-0405001-11
模式是光纤光学中的基本概念,也是光纤激光器研究中最关注的问题之一。在一般的教材、文献中对模式的简并问题涉及较少,没有给出清晰、直观的物理图像。文中采用经典的电磁场理论,阐明了矢量模的简并度、标量模的简并度以及矢量模和标量模之间的简并关系。在弱导阶跃折射率光纤中,矢量模和标量模都是描述光场的正交完备基,矢量模[HE1n(o)、HE1n(e)]与标量模[LP0n(ye)、LP0n(xe)]描述的光场空间是2维的,矢量模[TE0n、 HE2n(o)、 HE2n(e)、 TM0n]与标量模[LP1n(yo)、 LP1n(ye)、 LP1n(xo)、LP1n(xe)]描述的光场空间是4维的,矢量模[EHm-1,n(o)、 EHm-1,n(e)、 HEm+1,n(o)、 HEm+1, n(e)]与标量模[LPmn(yo)、LPmn(ye)、LPmn(xo)、LPmn(xe)]描述的光场空间也是4维的。  相似文献   

13.
It is shown that due to the similarity of the structures of the TEM cell and the finned waveguide, the closed-form expression for the cutoff frequency of the TE10 mode in the finned waveguides can be used to calculate the cutoff frequency of the TE01 mode in the symmetric TEM cells. The results obtained by the expression given agree with various numerical methods to within 1%. The results calculated by this expression are compared with those obtained by an approximate analytical expression  相似文献   

14.
Cylindrical and rectangular dielectric resonator antennas (DRAs) using HEM11δ, TE11δ, and TE01δ mode were examined to see the radiation pattern, impedance, field distribution and resonant frequency that were achieved when the DRAs were bisected through an image plane by a conducting sheet. The resultant half DRAs are smaller in volume and have a more directional radiation pattern. The elevation angle of maximum radiation was lowered in some cases. Finite-difference time-domain simulation techniques were used  相似文献   

15.
An asymptotic form of the characteristic equation that describes wave propagation at near-infrared wavelengths in small core hollow circular waveguides is developed. Analytic solutions for the transverse and axial propagation constants are obtained. These demonstrate the transition of the TE11 and TM01 modes to surface waves as the guide radius is increased to values much greater than at cutoff. Relative power density distributions illustrating these mode transitions are shown  相似文献   

16.
This letter presents an algorithm for suppressing the cross polarization of single offset reflector antennas illuminated by a cluster of multimode horn feeds using a constrained minimization routine. The design variables are the mode ratios for the higher order modes excited in the feeds relative to the dominant TE11 mode. The goal is to systematically determine the optimum mode ratios such that the overall crosspole performance of the reflector antenna improves relative to the single TE11 mode excitation. The multimode horns considered are Potter-type (dual mode) horns and trimode horns  相似文献   

17.
A new millimeter-wave omnidirectional dielectric rod metallic grating antenna is investigated theoretically and experimentally, in this paper. The radiation characteristics of the antenna are carefully investigated by a rigorous formulation for the TE01-mode and TM01-mode excitation in the Ka-band frequency range. Based on the analysis, an omnidirectional antenna excited by the TE01 mode is designed and measured. The measured results are compared with theoretical predictions and good agreement is found. Extensive numerical results are given to establish some useful guidelines for the design of the omnidirectional antenna  相似文献   

18.
An application of a numerical method of finite differences in the time domain (FDTD) coupled with the discrete Fourier transform is presented to determine the resonant frequencies of the TE0 and TM0 modes of axially symmetric dielectric resonators closed in a cavity. The technique is conceptually and computationally simple, and it allows access at once to information on the entire modal spectrum by means of the fast Fourier transform (FFT) applied to the time series. The cylindrical cavity dielectrically loaded at the base and the resonant frequency of the TE01δ mode are analyzed in two systems: a cylindrical cavity with a cylindrical dielectric resonator of variable radius, and the shielded dielectric resonator on a microstrip substrate. The results obtained are compared with the rigorous (exact) theoretical solutions and with experimental results  相似文献   

19.
A study of the dispersion characteristics of cylindrical metal-clad optical waveguides indicates that: (1) the propagation of electromagnetic energy in metal-clad optical waveguides differs in principal from that of dielectric step-index waveguides and ideal metallic waveguides; (2) hybrid modes exist in this structure, and the cutoff frequency of the HE11 mode does not equal zero; (3) TM and HE(EH) modes have attenuation higher at least by an order of magnitude than that of TE modes; and (4) the surface plasma wave can propagate in this structure. Thus, the lowest order mode is TE01   相似文献   

20.
An electrooptic Bragg diffraction modulator with high diffraction efficiency which utilizes a low-loss epitaxial ZnO optical waveguide on a sapphire substrate is discussed. An interdigital electrode with a spatial period of 20 μm and an aperture of 3 mm was fabricated directly on the film surface using a photolithographic technique. For the TE0 mode at 6328 Å, a maximum diffraction efficiency of 98% has been obtained from DC to 100 kHz with an applied voltage of about 31 V. The unclamped electrooptic coefficient r 33 is estimated to be 5.8×10-12 m/V which is much larger than the clamped value of 2.6×10-12 m/V in the literature  相似文献   

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